[41.19] Spectroscopy of comets Lee and LINEAR S4 in the 3 micron region using NIRSPEC

We present results of spectroscopic observations of C/1999
H1 Lee on UT August 21.6, 1999 and C/1999 LINEAR S4 on UT
July 13.4, 2000. The data were obtained using the NIRSPEC
instrument at the Keck II telescope atop of Mauna Kea, HI.
The NIRSPEC instrument is a cross-dispersed cryogenic
infrared spectrometer which permits a nearly complete
high-dispersion survey of the 2.9 - 3.7 \mum region. The 3
\mum region (3335 cm-1 - 3285 cm-1) includes
emission from HCN, C2H2, OH, NH2, and strong lines
that are preliminarily consistent with the 2\nu1 -
\nu1 band of H2O.

Thirteen lines of HCN were detected in comet Lee, permitting
an accurate determination of its rotational temperature (72
± 8 K) and production rate (2.9 ± 0.2) x 1026
molecules/sec. This production rate corresponds to a
relative abundance to water of (0.23 ± 0.02)%. Three
lines of C2H2 were also detected corresponding to a
production rate of (3.4 ± 0.3) x 1026
molecules/second and a C2H2/H2O relative abundance
of (0.27 ± 0.3)%.

Comet LINEAR S4 was observed under high humidity. Thus, many
lines that normally would have been clear of absorption,
fell in regions of low atmospheric transmittance. A few
relative strong emission lines were detected in the
spectrum, but do not correspond with HCN or C2H2. A
full analysis of this spectrum will be presented.

This research is supported by NSF grant no. 9619461 through
the Research at Undergraduate Institutions Program.